Header design for implantable pulse generator

ABSTRACT

In one embodiment, an implantable pulse generator for electrically stimulating a patient comprises: a metallic housing enclosing pulse generating circuitry; a header mechanically coupled to the metallic housing, the header adapted to seal terminals of one or more stimulation leads within the header and to provide electrical connections for the terminals; the header comprising an inner compliant component for holding a plurality of electrical connectors, the plurality of electrical connectors electrically coupled to the pulse generating circuitry through feedthrough wires, wherein the plurality of electrical connectors are held in place in recesses within the compliant inner component, the header further comprising an outer shield component adapted to resist punctures, the outer shield component fitting over at least a portion of the inner compliant component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/910,941, filed Apr. 10, 2007, the disclosure of which is incorporatedherein by reference.

TECHNICAL FIELD

The present application is generally related to a header design for animplantable pulse generator for accepting one or more stimulation leads.

BACKGROUND

Neurostimulation systems are devices that generate electrical pulses anddeliver the pulses to nerve tissue to treat a variety of disorders.Spinal cord stimulation (SCS) is an example of neurostimulation in whichelectrical pulses are delivered to nerve tissue in the spine for thepurpose of chronic pain control. Other examples include deep brainstimulation, cortical stimulation, cochlear nerve stimulation,peripheral nerve stimulation, vagal nerve stimulation, sacral nervestimulation, etc. While a precise understanding of the interactionbetween the applied electrical energy and the nervous tissue is notfully appreciated, it is known that application of an electrical fieldto spinal nervous tissue can effectively mask certain types of paintransmitted from regions of the body associated with the stimulatednerve tissue. Specifically, applying electrical energy to the spinalcord associated with regions of the body afflicted with chronic pain caninduce “paresthesia” (a subjective sensation of numbness or tingling) inthe afflicted bodily regions. Thereby, paresthesia can effectively maskthe transmission of non-acute pain sensations to the brain.

Neurostimulation systems generally include a pulse generator and one ormore leads. The pulse generator is typically implemented using ametallic housing that encloses circuitry for generating the electricalpulses, control circuitry, communication circuitry, a rechargeablebattery, etc. The pulse generation circuitry is coupled to one or morestimulation leads through electrical connections provided in a “header”of the pulse generator. Specifically, feedthrough wires typically exitthe metallic housing and into a header structure of a moldable material.Within the header structure, the feedthrough wires are electricallycoupled to annular electrical connectors. The header structure holds theannular connectors in a fixed arrangement that corresponds to thearrangement of terminals on a stimulation lead. When a stimulation leadis properly inserted within a port of the header, each terminal of thelead contacts one of the annular electrical connectors and, thereby, iselectrically coupled to the pulse generating circuitry through thefeedthrough wires.

A number of fabrication issues are associated with the selection of thematerial for the header. If a non-compliant high durometer material isselected for the header, additional complexity is typically provided tothe header design to hold the electrical connectors in place. Also, theplacement of the electrical connectors in such a header can be undulydifficult. Alternatively, if a compliant material is selected for theheader, the header can be easily punctured or otherwise damaged bysurgical tools during an implantation procedure.

SUMMARY

In one embodiment, an implantable pulse generator for electricallystimulating a patient comprises: a metallic housing enclosing pulsegenerating circuitry; a header mechanically coupled to the metallichousing, the header adapted to seal terminals of one or more stimulationleads within the header and to provide electrical connections for theterminals; the header comprising an inner compliant component forholding a plurality of electrical connectors, the plurality ofelectrical connectors electrically coupled to the pulse generatingcircuitry through feedthrough wires, wherein the plurality of electricalconnectors are held in place in recesses within the compliant innercomponent, the header further comprising an outer shield componentadapted to resist punctures, the outer shield component fitting over atleast a portion of the inner compliant component.

The foregoing has outlined rather broadly certain features and/ortechnical advantages in order that the detailed description that followsmay be better understood. Additional features and/or advantages will bedescribed hereinafter which form the subject of the claims. It should beappreciated by those skilled in the art that the conception and specificembodiment disclosed may be readily utilized as a basis for modifying ordesigning other structures for carrying out the same purposes. It shouldalso be realized by those skilled in the art that such equivalentconstructions do not depart from the spirit and scope of the appendedclaims. The novel features, both as to organization and method ofoperation, together with further objects and advantages will be betterunderstood from the following description when considered in connectionwith the accompanying figures. It is to be expressly understood,however, that each of the figures is provided for the purpose ofillustration and description only and is not intended as a definition ofthe limits of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an implantable pulse generator that includes a headeraccording to one representative embodiment.

FIGS. 2A and 2B depict known electrical connectors that can be utilizedwithin a header according to representative embodiments.

FIG. 3 depicts a compliant inner component of a header according to onerepresentative embodiment.

FIG. 4 depicts a shield component of a header according to onerepresentative embodiment.

FIG. 5 depicts a structure for holding an antenna in a helical manneraccording to one representative embodiment.

FIG. 6 depicts a schematic of an equivalent circuit for an antennaaccording to one representative embodiment.

DETAILED DESCRIPTION

Some representative embodiments are directed to a header design for aneurostimulation system. The header design preferably comprises acompliant silicone component and a shield component of a non-compliantmaterial. The silicone component and the shield component cooperate toprovide seals between the lead electrodes and to provide a barrier toprotect against damage or punctures from surgical tools used duringimplantation. The header design also preferably comprises an antennacomponent that defines a helical antenna path to support RFcommunications. Also, the antenna component is preferably adapted tofacilitate coupling of the antenna with tissue of the patient to achievea greater communication range for the implantable pulse generator.

FIG. 1 depicts implantable pulse generator 100 according to onerepresentative embodiment. Implantable pulse generator 100 comprisesmetallic housing 110 that encloses the pulse generating circuitry,control circuitry, communication circuitry, battery, etc. of the device.An example of pulse generating circuitry is described in U.S. PatentPublication No. 20060170486 entitled “PULSE GENERATOR HAVING ANEFFICIENT FRACTIONAL VOLTAGE CONVERTER AND METHOD OF USE,” which isincorporated herein by reference. A microprocessor and associated chargecontrol circuitry for an implantable pulse generator is described inU.S. Patent Publication No. 20060259098, entitled “SYSTEMS AND METHODSFOR USE IN PULSE GENERATION,” which is incorporated herein by reference.Circuitry for recharging a rechargeable battery of an implantable pulsegenerator using inductive coupling with an external charging device isdescribed in U.S. patent Ser. No. 11/109,114, entitled “IMPLANTABLEDEVICE AND SYSTEM FOR WIRELESS COMMUNICATION,” which is incorporatedherein by reference. An example of a commercially available implantablepulse generator that may be adapted to include a header according tosome representative embodiments is the EON® implantable pulse generatoravailable from Advanced Neuromodulation Systems, Inc.

As shown in FIG. 1, header 120 comprises compliant inner component 121,non-compliant shield component 122, and antenna component 123. Compliantinner component 121 is preferably fabricated using an injection moldingprocess and silicone based materials. Compliant inner component 121 isadapted to receive two stimulation leads (not shown) through strainrelief elements 132, although header 120 could be alternatively adaptedto couple to any suitable number of stimulation leads. To minimize theprofile of implantable pulse generator 100, compliant inner component121 is adapted to receive the stimulation leads in a side-by-side mannerin one embodiment. Other embodiments may be configured to receive thestimulation leads in an above-below manner or even in an array-likemanner for several stimulation leads.

Compliant inner component 121 is adapted to hold a plurality ofelectrical connectors 131 for each stimulation lead. Specifically,compliant inner component 121 comprises a plurality of recesses definedbetween respective wall structures 135 in which electrical connectors131 are disposed. The compliant material characteristic of component 121holds electrical connectors 131 in place by applying an elastomericforce. Electrical connectors 131 are spaced apart in relation to thespacing of the terminals of the stimulation leads intended to functionwith implantable pulse generator 100. Each electrical connector 131 iselectrically coupled to pulse generation circuitry within metallichousing 110 through a respective feedthrough wire as is known in theart. Compliant inner component 121 is shown in isolation in FIG. 3.Apertures 301 within walls 135 are shown in FIG. 3 for the respectivestimulation leads.

Typically, electrical connectors 131 are fabricated using an outerconductive annular or ring-like structure. Within the ring-likestructure, one or more conductive members are held to engage arespective terminal of the stimulation lead. An example of knownconnector 200 is shown in FIG. 2A in which a canted spring is heldwithin a conductive ring. Such connectors are commercially availablefrom Bal Seal, Inc. of Foothill Ranch, Calif. Another example of knownconnector 250 is shown in FIG. 2B in which a conductive disk havingarcuate connector tabs is held within a conductive ring as shown in U.S.Patent Publication No. 20050107859, entitled “SYSTEM AND METHOD OFESTABLISHING AN ELECTRICAL CONNECTION BETWEEN AN IMPLANTED LEAD AND ANELECTRICAL CONTACT,” which is incorporated herein by reference. It shallbe appreciated that other types of electrical connectors could beemployed such as “block electrical connectors” which are known in theart. Also, different types of electrical connectors could be employedwithin the same header in any suitable configuration.

Shield component 122 (shown in isolation in FIG. 4) is adapted to fitover a significant portion of and mechanically couple to inner compliantcomponent 121. Shield component 122 may also be adapted to fit over aportion or all of antenna component 123. When header 120 is fullyassembled and stimulation leads are placed in header 120 through strainrelief elements 132, the various conductive elements are sealed withinthe components of header 100. Specifically, when implantable pulsegenerator 100 is implanted within a patient, the electrical componentsare sealed and are prevented from contacting bodily fluids.Additionally, shield component 122 is fabricated from a relatively hardmaterial to prevent damage to or puncture of compliant inner component121. Specifically, if a sharp object used during the implantationprocedure were to contact compliant inner component directly, compliantinner component 121 could be punctured somewhat easily. The puncturecould allow entry of body fluids and cause the patient to experienceelectrical stimulation in the subcutaneous implantation pocket. Byutilizing a suitable material for shield component 122, compliant innercomponent 121 is protected from sharp surgical tools, needles, staples,and the like. An example of a suitable material for shield component 122is a relatively high durometer Bionate® polycarbonate urethane.

Header 120 comprises antenna component 123 to facilitate RFcommunication between the implantable pulse generator 100 and anexterior controller device (not shown). The exterior shell of antennacomponent 123 is preferably a relative high durometer polymer. In onepreferred embodiment, the exterior shell of antenna component 123 is arelatively high durometer Bionate® polycarbonate urethane. Platinumribbon 133 forms the actual far field antenna and is preferably wrappedaround a helical path defined within the interior of antenna component123. Preferably, the antenna and communication circuitry enable wirelesscommunications within a range of several meters. In one embodiment,platinum ribbon 133 is wrapped around molded polymer component 501(shown in FIG. 5) which is enclosed within the exterior shell of antennacomponent 123. Polymer component 501 may provide any suitable number ofrevolutions for antenna ribbon 133.

Referring again to FIG. 1, platinum ribbon 133 is coupled tocommunication circuitry within metal housing 110 through feedthrough134. The upper segments of platinum ribbon 133 are disposed immediatelybelow slots 136 of exterior shell of antenna component 123. Slots 136are formed by reducing the thickness of the polymer material of theexterior shell at the appropriate locations. The reduced thickness ofthe polymer material at these locations promotes the efficiency of thecoupling of the RF signal with tissue of the patient. Such couplingfacilitates a greater communication range for the RF signal.

Antenna 123 is preferably fully insulated from contact with human tissueby header 120 so that no corrosion products from the conductor of theantenna enter tissue, and, there is little surface impedance variationcaused by fibrosis, scar tissue, etc, after implant. Surface impedancevariation on the conductor may cause the distribution of radiatingcurrent density to change, possibly in a manner which deleteriouslyaffects the radiation pattern outside the human body. Furthermore, grosssurface impedance alterations may alter the amount of totalelectromagnetic energy radiated from/or into the antenna by causingintended emitted/absorbed energy to be reflected back to thetransmitter.

The skewed cross-section shape of antenna 123 is preferably an invertedtriangle with finite radius curves replacing triangle vertices. In oneembodiment, the lowest, rounded, vertex is designed to be furthest fromthe straight top segment of each section, so that the enclosed areamaximizes the storage of magnetic energy. But it is not so close to theconductive (“ground”) surface of the enclosure that coupling to theenclosure is more than a small fraction of the coupling from the topsegment to tissue. In that way, RF displacement current is provided witha lower impedance path from top segments of the antenna, much lower thanthat between lowest rounded vertices.

In some embodiments, the lowest rounded vertices may have any radius ofcurvature up to and including half the width of header 120. Or, as smallas the minimum bend radius of conductor 133 according to someembodiments. However, as the radius of vertex curvature decreases, theRF electric field flux density increases in proximity to that vertex.The coupling to the enclosure would increase, and so to compensate thosevertices would have to be displaced closer to the top segments ofantenna 123. This would reduce the magnetic energy storage(“inductance”) of each spiral revolution, or “turn” of the antenna. Theintent of some embodiments is to optimize the inductance per turn withthe (“electrostatic”) coupling between turns so that the overallimpedance of the antenna maximizes coupling into human tissue along thetop sections of antenna 123, while also presenting an easily-matchedimpedance at the antenna feed terminal. The schematic 600 (FIG. 6) showsthe approximate lumped element equivalent circuit.

The intent of some embodiments is to enhance emission from the top ofthe antenna, with a return path through human tissue, such that thecurrent density distribution maximizes radiation outside the human body.The alignment of antenna 123 is preferably adapted such that directionsof maximum radiation power density tend to be located symmetricallyeither side of the antenna mid-plane. The optimum electric fieldpolarization direction is transverse to the antenna mid-plane. Therewould be a null (minimum) of the transverse polarization radiationintensity in the antenna mid-plane, provided the surrounding medium(human tissue) was isotropic and homogeneous.

Each complete path (“revolution”) of inverted triangle with curvedvertices, mentioned above, connects conductively with the adjacenttriangular paths at one location, so that the complete antenna consistsof multiple inverted triangular spiral elements connected together. Theapproximate equivalent circuit is shown in FIG. 6, for the example of asix turn inverted triangular spiral antenna (6T ITSA).

The conductor 133 of antenna 123 preferably consists of a metal strippresenting a large surface area along the top segments of the antenna,so that capacitances (C12-17, above) are maximized for a given thicknessof insulation (dielectric), having a certain dielectric constant. Forexample, a rectangular cross section with a surface resistance per unitarea much less than the surface reactances per unit area, presented byC12-17, at the radio frequency of operation.

Although certain representative embodiments and advantages have beendescribed in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the appended claims. Moreover, the scope of thepresent application is not intended to be limited to the particularembodiments of the process, machine, manufacture, composition of matter,means, methods and steps described in the specification. As one ofordinary skill in the art will readily appreciate when reading thepresent application, other processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the described embodiments maybe utilized. Accordingly, the appended claims are intended to includewithin their scope such processes, machines, manufacture, compositionsof matter, means, methods, or steps.

1. An implantable pulse generator for electrically stimulating a patient, comprising: a metallic housing enclosing pulse generating circuitry; and a header mechanically coupled to the metallic housing, the header adapted to seal terminals of a plurality of stimulation leads within the header and to provide electrical connections for the terminals, the header comprising an outer shield component, a plurality of electrical connectors electrically coupled to the pulse generating circuitry through feedthrough wires, and an inner compliant component; wherein (i) the inner compliant component is an integral, single piece of compliant material, (ii) the inner compliant component comprises a plurality of walls defining a plurality of recesses, (iii) the plurality of electrical connectors are held in the plurality of recesses by an elastomeric force applied by the plurality of walls, (iv) the plurality of walls comprise a plurality of apertures defining two respective parallel channels through the inner compliant component, and (v) the outer shield component is fit over at least a portion of the inner compliant component containing the plurality of electrical connectors to protect the inner compliant component from punctures from surgical implant tools; wherein (i) the header further comprises an antenna component that comprises an exterior shell enclosing an antenna for far field communications, (ii) the antenna comprises a plurality of discrete turns disposed in a substantially planar orientation relative to a top portion of the exterior shell, (iii) the exterior shell comprises a plurality of slots having reduced thickness in the exterior shell, and (iv) the discrete turns of antenna are disposed immediately beneath the plurality of slots of the exterior shell.
 2. The implantable pulse generator of claim 1 wherein the compliant inner component is fabricated using a silicone-based material.
 3. The implantable pulse generator of claim 1 wherein the outer shield component is fabricated using a relatively high durometer polycarbonate urethane material.
 4. The implantable pulse generator of claim 1 wherein the inner compliant component comprises one or more strain relief components for receiving one or more stimulation leads.
 5. The implantable pulse generator of claim 1 wherein the exterior shell is adapted to couple RF power from the antenna to fluid or tissue of the patient when the implantable pulse generator is implanted within the patient.
 6. The implantable pulse generator of claim 1 wherein the exterior shell of the antenna component is fabricated using a relatively high durometer polycarbonate urethane material.
 7. The implantable pulse generator of claim 1 wherein the antenna component comprises an inner molded structure around which the antenna is wound.
 8. The implantable pulse generator of claim 1 wherein the antenna is a helical antenna. 